... then they say that there will be a raffle held from all ticket holders for only certain ones to attend the book signing

From what I have heard there is no such thing [anymore] as Mr. King sitting behind the table in a book shop with a long queue of people bringing books to have them signed.
He sells pre-signed books (for significantly more than they cost un-signed). In your case it might be that he won't be selling those but a raffle would select who receives signed book.
If you think about it, when a relatively unknown author comes to a store to do a book signing, relatively few people would show up. If Stephen King announced that he would be signing books somewhere, the queue would be miles and miles long.